The present invention relates to lubricant grease for low and high temperature application and to a rolling bearing. More particularly, the present invention relates to the lubricant grease that can be applied suitably for electric auxiliaries used for cars at low and high temperatures and the rolling bearing.
The lubricant grease is sealed in the rolling bearing to impart lubricant property thereto. The lubricant grease is obtained by kneading abase oil and a thickening agent both serving as its main component. As the base oil, mineral oil and synthetic oil such as ester oil, silicone oil, and ether oil are used. As the thickening agent, metal soap such as lithium soap and urea compounds are generally used. The lubricant grease contains additives such as an antioxidant, a rust preventive, a metal deactivator, and a viscosity index improver as necessary.
In recent years, there are growing demands for production of a car which is compact, lightweight, and has low degree of noise. Therefore efforts are made to produce electric component parts for the car which are compact, lightweight, and have low degree of noise and make the interior of the engine room airtight. To do so, the electric component parts are required to have high output and efficiency. Because the life of the lubricant grease to be sealed in the rolling bearing is shorter than the life of the rolling bearing caused by its fatigue, the life of the rolling bearing depends on the life of the lubricant grease. Therefore the temperature to which the lubricant grease used for electric auxiliaries is resistant should be higher than the temperature to which urea-containing lubricant grease is resistant.
Heretofore heat-resistant fluorine-containing lubricant grease containing fluorocarbon resin powder as its thickening agent and perfluoropolyether oil as its base oil is used as grease to be sealed in the rolling bearing for use in a fan clutch which is heated to high temperatures in the neighborhood of 200° C. But the fluorine-containing lubricant grease is expensive and prevents reduction of the cost of the rolling bearing.
Therefore hybrid grease containing a mixture of the fluorine-containing lubricant grease and the urea-containing lubricant grease has been developed, as disclosed in Japanese Patent Laid-Open Nos. 2002-327759, 2004-3596, and 2004-26941. A lubricant grease composition having a preferable noise-reducing effect at temperatures of 180° C. to 250° C. is also known, as disclosed in Japanese Patent Laid-Open No. 2000-514105.
However, the conventional fluorine-containing lubricant grease generates noises at low temperatures when the fluorine-containing lubricant grease is used for electric auxiliaries.
When the viscosity of the base oil is reduced to restrain noises from being generated at low temperatures by the fluorine-containing lubricant grease, noises are decreased at low temperatures. But the fluorine-containing lubricant grease containing the base oil is not durable at high temperatures in the neighborhood of 200° C.